The long range goal of this proposal is to characterize the molecular and functional properties of monoclonal antibodies (MoAb) elicited by antiidiotypic MoAb which bear the internal image of human high molecular weight-melanoma associated antigen (HMW-MAA) and GD3 ganglioside. The latter two antigens are being used as targets for immunotherapy in patients with melanoma. The outlined studies will take advantage of a unique panel of antiidiotypic and antiantiidiotypic MoAb elicited during the previous grant period. We will analyze the genetic control of the humoral anti HMW- MAA immune response elicited y the antiidiotypic MoAb elicited with MoAb MK2-23 which bears the internal image of HMW-MAA. This information may suggest criteria to select patients who are likely to mount an anti HMW-MAA immune response following immunization with MoAb MK2-23. We will define the molecular basis of the specificity of antiantiidiotypic MoAb elicited with MoAb MK2-23 by correlating their antigen binding activity with the sequence of the variable regions of their heavy and light chains. Sequences may be identified which are potentially important for HMW-MAA binding activity of MoAb. We will humanize the mouse antiidiotypic MoAb MK2-23, which is being used as an immunogen in clinical trials, to overcome the problem of the formation of antimouse Ig antibodies. We will analyze the immunogenicity of humanized MoAb MK2-23, since this information will be useful to optimize the immunization schedule in patients with melanoma. We will characterize antiidiotypic MoAb elicited with the anti GD2 ganglioside MoAb MB3.6 and we will identify those which bear the internal image of CD3 ganglioside. We will correlate the sequences of the variable regions of the heavy and light chains of antiidiotypic MoAb with their immunogenic properties to define the structure-function relationship of these molecules. Lastly, we will determine the ability of antiidiotypic MoAb to modulate the immune lysis of melanoma cells mediated by anti GD3 ganglioside antibodies. the outlined studies will provide for the first time information about the structural and functional characteristics of the idiotype cascade in the HMW-MAA and in the GD3 ganglioside systems. Furthermore, the potential role of the idiotypic network in the effect of anti GD3 ganglioside immunity on the course of the disease will be characterized.